The present invention is directed to bicycle drive mechanisms and, more particularly, to a multiple sprocket assembly for a bicycle which includes a large number of freewheel sprockets.
FIG. 1 is a diagram illustrating a typical bicycle chain drive mechanism. As shown in FIG. 1, crank arms 1 having pedals 3 are rotatably coupled to a bicycle frame 2. A chainwheel assembly C comprising a plurality of sprockets, for example, C1 and C2, are connected to crank arms 1 so that rotating pedals 3 in a circular manner causes sprockets C1 and C2 to rotate together with crank arms 1. A freewheel assembly F comprising a plurality of sprockets F1, F2, etc. are mounted to the rear wheel of the bicycle (not shown), and a chain 4 selectively engages one of the chainwheel sprockets and one of the freewheel sprockets. A front derailleur 5 having a chain guide 6 is provided to switch the chain among the plurality of chainwheel sprockets, and a rear derailleur 7 having a guide pulley 8 and a tension pulley 9 is provided to switch the chain among the plurality of freewheel sprockets.
It is desirable to increase the number of sprockets, particularly in the rear freewheel, to provide the bicyclist with a greater choice of gears. However, the amount of lateral space in which to mount the chainwheel and/or freewheel is limited by the design of the bicycle and accepted design standards. Thus, in order to fit more sprockets into the available space, it is usually necessary to decrease the spacing between the adjacent sprockets. On the other hand, the minimum spacing between adjacent sprockets is limited by the width of the chain.
FIG. 2 is a top view of a segment of the conventional chain 4. A typical chain has pairs of outer links 10A and 10B which alternate with pairs of inner links 11A and 11B, wherein each pair of outer links 10A and 10B is connected to a corresponding pair of inner links 11A and 11B using a press-fit connecting pin 12. More specifically, the ends of each outer link 10A and 10B and the ends of each inner link 11A and 11B have openings for receiving connecting pin 12 therethrough. The corresponding ends of one pair of outer links 10A and 10B are aligned with the ends of an associated pair of inner links 11A and 11B, with the inner links 11A and 11B disposed laterally inwardly of the outer links 10A and 10B, so that the openings in the ends are aligned with each other. The ends of inner links 11A and 11B include flange sections 11C and 11D which abut each other and define the openings of inner links 11A and 11B. A roller 13 is disposed between the pair of inner links 11A and 11B and is rotatably supported by flange sections 11C and 11D. The connecting pin 12 passes through the opening in each link end 10A, 10B, 11A, and 11B such that the connecting pin 12 is press fit in the outer link ends 10A and 10B.
The lateral width of a typical chain 4 thus equals the top width of two outer links 10A and 10B plus the top width of two inner links 11A and 11B plus the width of the roller 13 (which is approximately equal to the width of the flange sections 11C and 11D). As a result, the number of sprockets in the multiple freewheel assembly is limited accordingly. More specifically, the minimum spacing between adjacent sprockets is equal to the thickness of one inner chain plate plus the thickness of one outer chain plate plus the thickness of the laterally projecting portion of the connecting pin plus a small free area to avoid binding of the chain, the sum of which is approximately equal to 2.8 millimeters.